1. Field of the Invention
This invention relates to an electro-chargeable fiber and more particularly relates to an electro-chargeable fiber that does not require a washing process to remove fiber finish, used for nonwoven processed products such as air filters and wipers.
2. Description of the Related Art
In recent years, concerns about spaces free of garbage, dust, and dirt have been enhanced, including buildings, underground areas, vehicles, amusement arcades, as well as clean rooms in laboratories and factories. To provide such spaces, there has been a growing demand for air filters collecting dust by using electrostatic properties of fibers. Synthetic fibers with electrostatic charge or nonwoven fabrics thereof are being used for these air filters.
The above nonwoven products are obtained generally using staple fibers or short-cut fibers as a starting material and forming a web thereform by a processing method such as a carding method or an air-laid method, followed by a heat adhesion or a mechanical entanglement thereof, and an electret treatment of the resulting nonwoven fabric. The electret treatment means that a process of heat-electret, corona discharge-electret and the like gives nonwoven fabrics an electrostatic charge in the forming process or after being formed.
The surfaces of fibers for a nonwoven fabric processing generally are supplied with a fiber finish (also referred to as finishing oil), such as a surfactant, in order to suppress adverse effects on processability and productivity of nonwoven fabric due to generation of electrostatic. However, for the above nonwoven products, such fiber finish disturbs the process of electret treatment, and lowers the dust-collecting efficiency over time as well.
Therefore, in the process of electret treatment of nonwoven fabric, there needs to be a secondary process for water or hot water washing, or a method of removing the fiber finish while entangling by a water-jet method, which presents problems such as restrictions in the process, increase in process facilities, and rising cost of production. A method of nonwoven fabric forming and electret treatment, by taking advantage of decreasing in fiber finish applied to fibers in a heat treatment process, is disclosed in patent reference 1. However, there are restrictions due to requirements of a heat treatment before the electret treatment and an advanced quality control technique to control the amount of fiber finish applied at below a given value.
Patent reference 1: Japanese patent application laid-open No. 2002-339256